Resonant Raman random lasing from disorder-structured material pumped by nanosecond-pulsed laser

Abstract

Raman spectroscopy can provide “chemical fingerprint”, unique for each chemical composition; nevertheless, spontaneous Raman scattering has low efficiency (10−8-10−10). In this study, we report the evidence of Raman random lasing (RRL) generated from disordered materials even pumped by a nanosecond-pulsed laser, resulting in enhancement of Raman signal. The 355 nm UV excitation pulses allowed higher Stokes intensity due to the resonant Raman effect, compensating for the comparatively wider pulse duration. For the experiment, the effects of sample packing densities on RRL efficiency were studied for Ba(NO3)2 powder. The RRL threshold of the loosely-packed structure was lower than the closely-packed structure, and the RRL power efficiency reached 4.25 × 10−4, for the former case. It is consistent with the coherent backscattering results that indicated the longer transport mean free path for the loosely-packed structure, implying deeper photon penetration into the sample structure with lower density. Furthermore, the full-wave simulation on COMSOL Multiphysics was solved for the investigation of localization time and confined energy of electromagnetic wave in the random structures. The closely-packed structure showed better localization property. However, the loosely-packed structure allowed more incident light to penetrate into the medium, which affected more profoundly on RRL generation.